如何更改绑定 WPF class 变量的值？

Question

I am new to WPF/XAML.

I am making a scrolling marquee using a demo I found online. It is WinForms using a HostedElement WPF custom User Control.

I was able to setup a class called MyModelView so that I can bind the text value of a textblock to a variable I control (MyTextProperty).

But I can't figure out how to change the variable. My goal is to have a textbox you can enter text into and it will bind to the textblock value and change it while the program is running.

I am not able to do this, which I am trying to do (Change bound variable to TextBox1 value - it is not a valid reference to the variable... what is?):

Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
    MyViewModel.MyTextProperty = TextBox1.text
End Sub

How do I reference that class variable to change the text? I am missing something.

MyViewModel.vb

Imports System.ComponentModel

Public Class MyViewModel
    Implements INotifyPropertyChanged

    Public Sub New()
        Me.myTextValue = "WINNING!!!"
    End Sub

    Private myTextValue As String = String.Empty
    Public Property MyTextProperty() As String
        Get
            Return Me.myTextValue
        End Get

        Set(ByVal value As String)
            Me.myTextValue = value
            NotifyPropertyChanged("MyTextProperty")
        End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler _
        Implements INotifyPropertyChanged.PropertyChanged

    Private Sub NotifyPropertyChanged(ByVal propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub

End Class

Scrolling Marque.xaml

<UserControl x:Class="ScrollingMarquee"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:interopdemo="clr-namespace:InteropDemo"
    mc:Ignorable="d" 
    d:DesignHeight="100" d:DesignWidth="300">
    <UserControl.Resources>
        <Storyboard x:Key="MarqueeScroll">
            <DoubleAnimation RepeatBehavior="Forever" 
                Storyboard.TargetProperty="(Border.RenderTransform).(TranslateTransform.X)" 
                Storyboard.TargetName="spMarquee" 
                From="1500"  To="-500" 
                Duration="0:0:0:7" />
        </Storyboard>
    </UserControl.Resources>
    <Grid>
        <Grid.DataContext>
            <interopdemo:MyViewModel/>
        </Grid.DataContext>
        <StackPanel x:Name="spMarquee" Orientation="Horizontal"  Width="Auto">
            <TextBlock Text="{Binding MyTextProperty}" FontSize="28" VerticalAlignment="Center" Margin="30,0,60,0"/>
            <TextBlock Text="Hello Scrolling Text!" Foreground="Firebrick" FontSize="28" VerticalAlignment="Center" Margin="40,0,60,0"/>
            <TextBlock Text="Ticker 2000!" Foreground="Red" FontSize="28" FontStyle="Italic" FontWeight="Bold" VerticalAlignment="Center" Margin="50,0,80,0"/>
            <StackPanel.RenderTransform>
                <TranslateTransform/>
            </StackPanel.RenderTransform>
        </StackPanel>
    </Grid>
</UserControl>

Form1.vb

Imports System.Windows.Media.Animation

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None
        Me.WindowState = FormWindowState.Maximized

        ElementHost1.Visible = True
        Dim storyRunMarquee As Storyboard = ScrollingMarquee1.FindResource("MarqueeScroll")
        storyRunMarquee.Begin()

    End Sub

End Class

I've tried referencing the variable but can't make it work. The scrolling animation displays as "Winning. Hello Scrolling Text! Ticker 2000!" But I'm trying to change the bound "Winning!" text.

Answer 1

Remove

<Grid.DataContext>
   <interopdemo:MyViewModel/>
</Grid.DataContext>

Declare a member variable in the form to hold reference to the view model object:

Private scrollerViewModel As MyViewModel

Instantiate an object of class MyViewModel in Form1_Load and set it as a DataContext for user control.

Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load
   Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None
   Me.WindowState = FormWindowState.Maximized

   ElementHost1.Visible = True

   scrollerViewModel = New MyViewModel
   ScrollingMarquee1.DataContext = scrollerViewModel

   Dim storyRunMarquee As Storyboard = ScrollingMarquee1.FindResource("MarqueeScroll")
   storyRunMarquee.Begin()

End Sub

Modify property:

Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
    scrollerViewModel.MyTextProperty = TextBox1.text
End Sub

Answer 2

I think you just need to cast the datacontext of ScrollingMarquee1 as MyViewModel

 CType(ScrollingMarquee1.DataContext, MyViewModel).MyTextProperty = TextBox1.text